Stereoscopic, long-distance microscope

ABSTRACT

A stereoscopic, long-distance microscope is capable of stereoscopically viewing targets within the range of 100 mm to 300 mm from the front lens element. The system preferably comprises: a front lens element having a diameter D fl  for receiving light rays from the target; a rear mirror having a diameter D rm  for receiving light rays from the front lens element; a secondary mirror located on the rear surface R 2  of the front lens element for receiving light reflected from the rear mirror element; and, an angled mirror located between the secondary mirror and the stereoscopic eyepiece in its turn receiving light rays reflected from said angled mirror and presenting them to both eyes of the viewer. The diameter D fl  of the front lens element is preferably significantly smaller than the diameter D rm  of the rear mirror element.

This application is a 371 of PCT/US99/03303 filed Feb. 19, 1999, whichclaims benefit of Provisional No. 60,078,146 filed Mar. 16, 1998.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention generally relates to an optical microscope and, inparticular, a stereoscopic, long-distance microscope having a target inthe range of 100 mm-300 mm from the front optical element of themicroscope.

2. Description of Related Art

The prior art includes a significant number of telescopes and the likethat have the following basic structure: a convex front lens; a concaverear mirror for receiving light from the front lens; a secondary mirrorlocated on the backside of the front lens for receiving light focusedfrom the rear mirror; an angled mirror, or the like, for receivingreflected light from the secondary mirror; and, an eyepiece for viewingthe image reflected from the angled mirror. The target is typicallylocated at a substantial distance from the front lens and the front lensand rear mirror have substantially the same diameter. An example of awell known telescope for observing astronomical events or observing orphotographing terrestrial events, is the Questar 3½ sold by the QuestarCorporation, 6204 Ingham Road, New Hope, Pa., 18938.

Other optical devices which include a compound refractive first frontlens, a concave primary rear mirror, a secondary mirror and a mechanismfor focusing the result onto an eyepiece are found in the followingpatent disclosures: U.S. Pat. Nos. 2,748,658; 2,726,574; 3,532,410; and,5,471,346.

U.S. Pat. Nos. 4,755,031 and 5,181,145 describe similar structures. Inparticular, U.S. Pat. No. 5,181,145 discloses a beam that is reflectedfrom a secondary, convex mirror which impinges on a beam splitterthereby producing two images at two different points. U.S. Pat. No.4,835,380 also describes the use of a beam splitter at the output end ofa similar structure.

The following patents disclose related structures, but without acompound refractive lens at the front end: U.S. Pat. Nos. 2,753,760;3,411,852; 3,468,597; 5,159,495; and, 5,161,051.

While the foregoing prior art disclosures have some nominal similarityto the present invention, nevertheless, none of them appear to describea structure or use which permits the device to be used as astereoscopic, long-distance microscope. Such a device can be especiallyuseful for unique applications such as neuro-surgery, high-speedmaterial processing and the inspection of complex materials for flawsand irregularities.

It was in the context of the foregoing need that the present inventionarose.

SUMMARY OF THE INVENTION

Briefly described, the present invention comprises a stereoscopic,long-distance microscope capable of imaging targets at a distancebetween 100 mm-300 mm from the front lens of the instrument whileproviding significant three-dimensional stereoscopic detail. Themicroscope basically comprises: a front compound convex refractory lenshaving a diameter D_(fl) for receiving light rays from the target; arear concave primary reflective mirror having a diameter D_(rm) forreceiving light rays from the front lens; a convex secondary mirrorlocated on the backside of the front lens for receiving light rays fromthe primary mirror; an angled plane or flat mirror for receiving thelight rays focused from the secondary mirror; and, a stereoscopiceyepiece for receiving the light rays from the angled mirror. Inaddition, an intermediate, convex lens may be located between thesecondary mirror and the angled mirror to further assist in the focusingof light rays from the front lens to the rear mirror. The diameterD_(fl) of the front lens is smaller than the diameter D_(rm) of the rearmirror. This combines with the location of the target within 100 to 300mm of the front lens to enable the front element to gather light at suchan angle from the target that extraneous light is eliminated from thelight bundles that emerge therefrom. The light bundles are refracted,focused, received and divided by the stereo eyepiece and finallycombined by the viewer into one three-dimensional image in the samefashion that normal eyes create one stereo image. The result is arealistic, three-dimensional view of an object located at a significantdistance from the front lens but greatly enlarged.

The invention may be more fully understood by reference to the followingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an elevated, cross-sectional view of the stereoscopic,long-distance microscope according to the preferred embodiment of theinvention.

FIG. 2 illustrates the different lengths that light rays travel betweenthe target and the front element of the apparatus and further indicatingthat a variety of different information about the target is inherentlycaptured by the different ray lengths.

FIG. 3A illustrates how rays from a red and green source are collectedrespectively in the right and left eyepieces of the system.

FIGS. 3B and 3C illustrate in greater detail how the green raysrepresenting the background objects focus earlier in the eyepieces ofthe system than the red rays which represent the foreground objects.

FIG. 3D represents the manner in which the green rays, representing thebackground objects, focus at a point earlier than the red rays.

FIG. 3E illustrates the opposite of FIG. 3D, namely that the red rays,which represent the foreground objects, focus later than the green rayswhich represent background objects.

FIG. 3F illustrates how rays from different sources, represented bydifferent colors, form a composite image at different focal points.

DETAILED DESCRIPTION OF THE INVENTION

During the course of this description like numbers will be used toidentify like elements according to the different figures thatillustrate the invention.

The invention 100, according to the preferred embodiment thereof, isillustrated in FIG. 1. The inventive system 100 depends for its accuracyand stereoscopic effectiveness on the fact that the target 10 is locatedwithin the prime focal range 12 of the optical system, namely 100 to 300mm. The location of the target 10, in turn, allows the front element of14 of the system to gather light at such an angle from the target 10,that extraneous light is eliminated from the light bundle 16 so that thelight bundle can, in turn, transfer to the main, rear, concave mirror 18only those rays which image the total target 10. The front element 14comprises a convex, refractory 25 lens having a diameter D_(fl) and asecondary mirror 22 located on the rear surface thereof. The rear mirror18 has a diameter D_(rm) which is necessarily greater than Dfl. Thepreferred range for D_(fl) is 55 to 75 mm and for D_(rm), 95 to 115 mm,with preferred values of D_(fl)=65 mm and D_(rm)=105 mm. Rays 20 are ofvaried lengths which are determined by the shape of the target 10. Thelarger, main, rear mirror 18 captures the variable-length rays 20 andreflects them to the secondary mirror 22 in such a way that the shape ofthe target 10 is maintained by the pattern which the rays 20 havecreated. This pattern shows the target 10 complete in depth. Thatinformation is further transmitted from the secondary mirror 22 by anangled flat mirror 24 to the two eye pieces 26 a and 26 b of thestereoscopic viewer 36, which are so placed that at the viewer'seye-level 28 that they are at the prime focal plane established by theoptics of the instrument 100. The complete information about the target10 conveyed by the light bundle can now be separated by the twostereoscopic eye pieces 26 so that the information conveyed by the righthalf of the ray bundle 30 can be distinguished by the eye from thatconveyed by the left half of the ray bundle 32. These images,collectively referred to as 34, are then combined by the viewer into onethree-dimensional image exactly as images are combined in the normal useof the eyes. The function of the observer's eyes in transmitting imagesto the optic nerves is thus central to the invention, because itconfirms the validity of the information pathway described from thetarget 10 to the combined images 34. This pathway is, in fact, an exactreplication of stereo vision in the eye, but with an image greatlyenlarged by means of the total optical system 100. The total system 100is thus an optical replication of the normal visual system when bothhuman eyes are involved.

The path followed by the light bundle 40 through the optical systemcontains and transmits the essential information about thethree-dimensional target 10. The distinction among the lengths of thevarious rays 40 a- 40 h becomes crucial at this point because theydisplay the contour of the target which is then available to the stereoeyepieces 26 a and 26 b as shown in FIG. 2. This may be best understoodby comparing with it once again the information provided normally by thetwo eyes of a human being. These receive three-dimensional images byrecording and combining through the optic nerves, the varied light-raylengths which describe the shape of an object. The contour of the objectis perceived because of these variable ray lengths; similarly theoptical system 100 sees and records these varied lengths and transmitsthem to the eyepieces 26 a and 26 b which then distinguish for the useof the eyes these varied lengths 40 a-40 h in the bundle of light rays.This is possible because the differing focus of the two eyepieces 26 aand 26 b as shown in FIG. 3 record sharply the rays of different lengthwhich have been conveyed to the eyepieces. These two eyepieces (26 a and26 b) can make use of the full information conveyed by the light bundles40 so that the observer 28 in turn sees the three-dimensional target 10in greatly magnified form.

The theory of operation of the stereo microscope reveals the fact that atarget 10 in close proximity to the unique optical system 100 produces astereoscopic image not available to optics designed to view more distanttargets.

If the target 10 was at any other distance—even as close as 9 or 10feet—the light rays 30 and 32 would transmit to the optic the image of aflat surface, because these rays 30 and 32 would be close enough toequal in length so that they could not record topographicaldistinctions. These would appear only as a plane surface image withwhatever depth of field the optic could capture. Note further that thiskind of depth would be the result of decreasing the aperture of the lens14 so that one sees objects before and behind the target focal planewith acceptable clarity; it is not stereo imaging.

An optical system 100, in order to capture stereo information, must meettwo (2) conditions: (a) it must have some distance from the target 10,but (b) it must not be too far from the target 10. An optic positionedvery close to the target 10 will clearly “see” only the rays that comedirectly toward it; an optic too far away will not distinguish thevariable ray lengths; as seen above they will at best become relativelyin focus. But within a restricted range, theory and practice meet, sothat distinctions of topography can be made and recorded. These, inturn, can be segregated by the independent focus of the eyepieces 26 aand 26 b so that the target 10 is observable in both its near and farcontours, which are then assembled by the eye 36 to give one compleximage. (It has already been indicated that great depth of field alonedoes not produce a true stereo effect). The stereo image is capturedbecause the optic transmits two essential types of information: first,it records the variations in length of the rays 30 and 32 observed, andsecond, it records oblique views of the target 10 which are determinedby variations in ray length. The curve of the front element 14 makesthis type of recording possible; all this information is then bothmagnified and distinguished by the optical sequence to give differentbut complementary information to the two stereo eyepieces.

The theory of operation is illustrated in greater detail in FIGS. 3A-3F.FIG. 3A illustrates rays from a red ray 50 and a green ray 52 separatedby five microns in the Z-axis. The binocular eyepieces 26 a and 26 bcollect the red 50 and green 52 rays for the right and left eye,respectively. It should be further noted that the precision of thisoptical sequence distinguishes it sharply from any superficial effectcreated by light dispersion. FIGS. 3B and 3C illustrate how the red rays50 are intercepted by the right eyepiece 26 a and the green rays 52 areintercepted by the left eyepiece 26 b. FIG. 3C, which is a continuationof FIG. 3B, illustrates how the green rays 52, which representbackground objects, focus earlier at a plane 54 located at 169.528 mmand how the red rays 50, which represent the foreground objects, focusat a further plane 56 located at 170.334 mm.

FIG. 3D essentially illustrates the same fact, namely that the greenrays 52 converge at plane 54 forming a focused background object. Inother words, the green rays are clustered closer to the center of thefocus than the red rays 50. Conversely, FIG. 3E illustrates thescattering and clustering of rays at the foreground plane 56, showinghow the red rays 50 are clustered and the green rays 52 are lessfocused.

Lastly, FIG. 3F illustrates how a composite object is formed from atleast four sets of rays of different colors.

The specific dimensions and relationships of the optical system 100 areaccording to the preferred embodiment:

Type: Maksutov Cassegrain Catadioptric

Working Range: Distance from target to front element—between 100 and 300mm

Open Aperture: 63.5 mm (or 2.5 inches)

Entrance Pupil: 104.14 mm (or 4.1 inches

Numerical Aperture/

Relative Aperture: Object Distance n.a. f/no 457.2 mm (or 18 inches).065 7.7 355.6 mm (or 14 inches) .083 6.0 254.0 mm (or 10 inches) .1154.3 152.4 mm (or 6 inches) .142 3.5

Spatial Resolution: Better than 1.25 microns at 150 mm, less than 1micron at 100 mm

Corrector Lens: BK-7, Magnesium Fluoride coated (standard), D_(fl)=63.5mm (or 2.5 inches) diameter where:

R₁=front surface of lens 14=58.5 mm

R₂=rear surface of lens 14=62.0 mm

T₁=midpoint thickness of lens 14=8.10±0.03 mm

Primary Mirror: Pyrex®, Aluminum coated, AISi04 overcoated,D_(rm)=104.14 mm (or 4.1 inches) diameter where:

T₂=distance from front lens element 14 to surface of rear mirror18=285.98±0.60 mm.

Secondary Mirror: R2 surface of corrector, Aluminum coated, AISi04overcoated, 16.5 mm (or 0.65 inches) diameter

Back Focal Distance: 2.75 inch minimum

Format: Diffraction limited field, 18 mm

Baffling: Helix in central tube, all interial surfaces anti-reflectionpainted

Barrel: 6061 Aluminum, machine from seamless stock, integrated lenscell, black anodized, length 254.0 mm (or 10 inches), outside diameter11.43 mm (or 4.5 inches, weight 2.57 kg (or 5 pounds).

In summary, this invention 100 employs a unique set of conditions toachieve its result. The target 10 rests within a critical range ofdistance (100-300 mm) from the front element 14 of the lens; rays 40 a-40 h from the target 10 thus diverge from the optical axis 42 at thespecific angles which record the contours of the target 10; the raypatterns created are both concentrated and amplified by the variouselements of the optical system 100 so that they become available to thetwo eyepieces 26 a and 26 b which are positioned to bring into threedimensional focus, the full array of light rays captured by the opticalsystem 100.

The present invention has several advantages over the prior art. First,the user can see a total object or target 10 in its full depth anddetail, whereas a prior art monoscopic view reduces the actual object toa two-dimensional approximation. Second, as a result, one can deriveinformation from certain highly critical procedures which requiredistance from the target and at the same time the ability to manipulateit without damage to either target or user. Examples would includeneuro-surgery, high-speed material processing, and the inspection ofcomplex materials for flaws and irregularities. For full effectiveness,all of these procedures require significant distance from the target andextreme resolution.

In order to achieve the foregoing, the present invention 10 has severalfeatures that are unique. First, the focal length of the microscope isneither directly adjacent to the front lens nor at a great distance suchas virtual infinity, but rather preferably in the range of 100 to 300mm. Accordingly, it is a true stereoscopic long-distance microscope.Second, the front lens element 14 is significantly smaller in diameterthan the rear lens element 18 (i.e., D_(rm)>D_(fl)) which, in part,permits focusing at distances such as 100 mm to 300 mm. The majorconsequence of this arrangement is the noticeable stereoscopic effectachieved.

While the invention has been described with reference to the preferredembodiment thereof, it will be appreciated that various modificationsmay be made to the structure and theory of the invention, withoutdeparting from the spirit and scope of the invention as a whole.

We claim:
 1. A stereoscopic, long-distance microscope apparatus (100)for stereoscopically examining a target (10), said apparatus (100)comprising: a front lens means (14) having a diameter D_(fl) forreceiving light rays from said target (10), said front lens means (14)having an object side surface and an image side surface; a rear mirrormeans (18) having a diameter D_(rm) for receiving light rays from saidfront lens means (14), said rear mirror means (18) having an object sidesurface that faces the image side surface of said front lens means (14),and wherein the diameter D_(fl) of said front lens means (14) is lessthan the diameter D_(rm) of said rear mirror means (18); a secondarymirror means (22) for receiving light rays from said rear mirror means(18), said secondary mirror means (22) being located on said image sidesurface of said front lens means (14); an angled-mirror means (24) forreceiving light rays from said secondary mirror means (22); and, aneyepiece means (36) for viewing the light rays from said angled mirrormeans (24), said eyepiece means (36) comprising a stereoscopic eyepiecesuitable for use by both eyes, wherein said light rays viewed by humaneyes through said eyepiece provide a stereoscopic, three-dimensionalview of said target (10) and wherein said target (10) is located within100 mm to 300 mm of said front lens means (14).
 2. The apparatus ofclaim 1 wherein said diameter D_(fl) of said front lens means (14) is inthe range of 55 to 75 mm.
 3. The apparatus of claim 2 wherein saiddiameter D_(rm) of said rear mirror means (18) is in the range of 95 to115 mm.
 4. The apparatus of claim 3 wherein said light rays cross pathsprior to impinging upon said eyepiece means (36).